1. Field of the Invention
The present invention relates to a time measurement device and a method for controlling the time measurement device. Particularly, the present invention relates to a time measurement device having a function of power saving and a function of receiving a radio wave bearing time information, and a method for controlling the time measurement device.
2. Description of the Related Art
A radio wave corrected watch having a power saving function is known as a time measurement device which has the function of saving power and the function of receiving a radio wave bearing time information. Japanese Unexamined Patent Application Publication No.11-223684 discloses such a radio wave corrected watch.
The radio wave corrected watch includes a current time counter for counting current time, time display means for displaying current time of the current time counter, receiving means for receiving a radio wave bearing time information, a power generator, a secondary battery storing power generated by the power generator, a voltage detector circuit for detecting a voltage from the secondary battery, and operation mode switching means for switching the operation mode of the time display means and a receiver circuit in response to the value of the detected voltage from the voltage detector circuit.
A long-wave time standard radio wave may be used as the radio wave bearing time information.
The power generator used for the device may be based on one that converts the force of a rotating weight into electrical power, one that performs photovoltaic generation, one that performs thermal generation using temperature differences, etc.
The radio wave corrected watch in the above arrangement works in a standard mode when the magnitude of the voltage detected by the voltage detector circuit is equal to or greater than a predetermined voltage magnitude. Specifically in the standard mode, the current time counted by the current time counter is displayed on the time display means. The receiving means receives the time information at predetermined time intervals. The current time of the current time counter is corrected in accordance with the received time information, and the time displayed on the time display means is also corrected.
When the voltage detected by the voltage detector circuit is lower than the predetermined voltage, the radio wave corrected watch works in a power saving mode. Specifically in the power saving mode, the supply of power to the current time counter, time display means, and receiving means is suspended. The power required to count the current time, display the time, and receive the time information is saved.
When the voltage detected by the voltage detector circuit rises above the predetermined voltage again, the device is switched from the power saving mode to the standard mode. The receiving means then receives the time information.
The time display means displays the current time based on the received time information.
When the voltage detected by the voltage detector circuit is lower than the predetermined voltage in this arrangement, power can be saved because the time is not displayed and the time information is not received.
When the magnitude of the voltage detected by the voltage detector circuit grows to be equal to, or greater than, the predetermined voltage again, the receiver receives the time information, and the current time in the current time counter is corrected accordingly. When the watch returns to the standard mode from the power saving mode, precise time based on the received time information is displayed.
There may be a case where the receiving means fails to receive the time information when the watch returns to the standard mode from the power saving mode. For example, if the radio wave corrected watch is in a building, the long-wave time standard radio wave may be blocked by the building walls and may fail to reach the watch's receiving means. As a second example, if a source of magnetic field is present surrounding the radio wave corrected watch, the long-wave time standard radio wave may be distorted by magnetic noise, and the watch may not be able to receive precise time information.
There is no mention in the above-quoted disclosure of the case in which the reception of the time information is unsuccessful, and the watch fails to switch to the standard mode from the power saving mode in this case. To know the current time, the user must wait until the time information is successfully received. This is quite an inconvenience.
The power saving function is required by not only a time measurement device having a power generator, but also a time measurement device driven by a primary battery. In particular, the radio wave corrected, watch which consumes a lot of power to receive the time information, requires a battery having longer service life.